1. Field of the Invention
The present invention relates generally to the field of medical devices and procedures and more particularly to the structure and deployment of embolic elements for occluding target sites, such as aneurysms, within a blood vessel.
Embolic coils, also referred to as vaso-occlusion coils, are used for selectively occluding blood vessels for a variety of purposes, such as the control of internal bleeding, the occlusion of blood supply to tumors, and the blocking of blood flow to aneurysms. Of particular interest to the present invention, embolic coils may be delivered to brain aneurysms by first positioning the distal end of a small tubular catheter through an opening in the blood vessel wall to the aneurysm and then pushing a plurality of embolic coils into the aneurysm volume. The coils then occlude the aneurysm by promoting thrombus formation.
While being generally successful, such treatment methods suffer from certain deficiencies. Most embolic coils display little or no expansion when they are released from their delivery catheters. One type of coil, which achieves perhaps the best expansion ratio, is delivered through the catheter as a straightened wire filament. Upon release from the catheter, the wire assumes a preset coil configuration within the aneurysm. The resulting coil, however, does not maximize the volume occupied by the embolic device. A second common approach relies on pushing an embolic coil through a delivery catheter with the coil in its coiled configuration. As the embolic coil is released, it further deploys with a secondary helical configuration, increasing the effective width of the coil, but decreasing its length. Again, the resulting occluded volume has not been maximized.
Conventional embolic coil delivery techniques also suffer from a lack of control. In many cases, the embolic coils are pushed through the distal end of the delivery catheter and released without any control over their positioning. While certain improvements have been proposed, such as where the embolic coil is attached to a pusher wire and released from the wire only after some positioning of the coil within the aneurysm, the control over positioning is quite limited.
It would therefore be desirable to provide improved embolic element structures and methods and apparatus for their delivery and deployment. In particular, it would be desirable to provide embolic element structures which possess both a compact delivery configuration and a maximally expanded released configuration in order to increase the occlusive volume of the element. It would be further desirable to provide embolic element delivery systems and methods which can control placement and positioning of the embolic element within a blood vessel target site, such as an aneurysm, prior to release of the embolic element into the site. It would be particularly desirable if the embolic element could be deployed in a preselected three-dimensional configuration prior to release into the site.
2. Description of the Background Art
Embolic coils and catheter delivery systems for such coils are described in U.S. Pat. Nos. 4,994,069; 5,108,407; 5,122,136; 5,217,484; 5,226,911; 5,234,437; 5,250,071; 5,261,916; and 5,312,415; and PCT applications WO 93/06503; WO 93/06884; WO 94/09705; WO 94/10936; and WO 94/11051. Endovascular placement of vascular appliances composed of shape memory materials is described in U.S. Pat. Nos. 3,868,956; 4,170,990; 4,503,569; 4,512,338; 4,950,258; and 5,067,957. The '956 patent described the in situ heating of vascular stents and filters to expand and anchor the devices within a blood vessel. Micro catheters and guidewires are described in U.S. Pat. Nos. 4,739,768; 4,813,934; 4,884,579; and 5,109,867.